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UNCLASSIFIED 


I.  Library 


Mechanical  Ventilation  and  Heating 

by  a 

Forced  Circulation  of  Warm  Air 

BY  f;  ; ’ 

:v  * .0^' 

WALTER  B.  SNOW 


A Lecture 

Delivered  at  Sibley  College,  Cornell  University 
November  17,  1899. 


/ 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/mechanicalventilOOsnow 


CATALOGUE  NO.  112. 


Published 


by  B.  F.  Sturtevant  Co.,  Boston,  Mass. 
Fourth  Edition,  1907. 


Asa  R.  Minard  & Company 
Incorporated 

34  Oliver  Street,  Boston,  Mass. 


MECHANICAL  VENTILATION  AND  HEATING 
By  a Forced  Circulation  of  Warm  Air. 


Walter  B.  Snow. 


In  the  combined  process  of  heating  and  ventilating,  a specific  amount  of 
heat  is  in  all  cases  required  to  compensate  for  transmission  losses  to  the  colder 
outdoor  atmosphere,  and  a certain  other  quantity  to  provide  for  the  warming  of 
all  air  which  intentionally  or  otherwise  enters  the  room  from  without. 

The  former  amount  varies  with  the  character  of  the  construction  and  the 
difference  between  indoor  and  outdoor  temperatures.  It  is  independent  of  the 
volume  of  air  supplied  for  ventilation.  The  amount  of  heat  required  for  tem- 
pering the  air  supply  for  ventilation  alone , is  directly  proportional  to  its  volume, 
and  is  that  necessary  to  raise  it  to  the  temperature  of  the  room.  This  is  in  no 
way  available  for  heating,  but  it  is  all  important  in  securing  satisfactory  ventila- 
tion, which,  when  properly  provided,  grows  effective  in  proportion  to  the 
expenditure. 

The  relative  costs  of  heating  and  of  ventilation  for  different  rates  of  air 
change  are  well  exemplified  in  the  accompanying  chart,  Fig.  i.  Here  as  is 
proper,  the  cost  of  mere  heating  is  shown  to  remain  constant,  but  the  necessary 
temperature  of  the  admitted  air  decreases,  while  the  cost  of  ventilation  increases 
with  the  volumes  admitted.  Inasmuch  as  a cold  room  will  not  be  tolerated, 
while  a vitiated  atmosphere  will  be  endured,  we  have  here  the  principal  reason 
why  so  few  buildings  are  well  ventilated,  namely,  the  cost  of  good  ventilation. 

We  are  not  to  assume,  however,  that  where  no  ventilation  is  intended  the 
fuel  expense  incurred  is  only  that  for  warming.  In  the  ordinary  dwelling 
heated  by  direct  means,  such  as  stoves,  steam  or  hot-water  radiators,  the  effect 
of  ventilation  resulting  from  infiltration  of  air  is  to  add  at  least  50  per  cent,  to 
the  mere  cost  of  warming.  Where  the  ventilation  is  intentional,  as  with  a fur- 
nace or  with  indirect  systems,  this  may  readily  mount  up  to  100  per  cent,  and 
\ over.  Therefore  in  the  consideration  of  more  effective  systems  of  ventilation, 


4 


MECHANICAL  VENTILATION  AND  HEATING. 


Fig.  i.  Relative  Costs  of  Heating  and  Ventilation,  with  Different 
Temperatures  of  Entering  Air. 


it  is  only  proper  to  consider  that  portion  of  their  expense  of  operation  which  is 
additional  to  that  of  existing,  although  inadequate,  systems. 

Viewed  in  this  light,  the  cost  of  securing  good  ventilation  is  by  no  means 
great,  while  its  improving  effect  upon  the  health  amply  warrants  its  introduc- 
tion. The  cost  of  ventilation  is  largely  dependent  upon  the  method  employed. 
Natural  ventilation,  either  through  Hues  or  by  leakage,  is  the  result  of  a differ- 
ence in  atmospheric  densities  and  pressures  due  to  internal  and  external  tem- 
perature differences.  Consequently  the  degree  of  ventilation  usually  varies 
with  the  outdoor  temperature,  and  is  lowest  when  that  is  highest.  Such  a 
method  is  therefore  absolutely  unstable. 

The  effectiveness  of  an  exit  flue  can  be  increased  by  warming  the  air 
within  by  means  of  gas  flames  or  steam  coils,  but  evidently  all  the  heat  thus 
imparted  represents  an  absolute  loss.  This  loss  can,  however,  be  almost 


MECHANICAL  VENTILATION  AND  HEATING. 


5 


entirely  avoided  by  the  employment  of  mechanical  means  for  producing  the 
necessary  air  movement.  The  most  effective  device  for  this  purpose  is  a fan 
blower.  Prof.  Carpenter  has  shown  by  the  accompanying  table  the  ratio  of 
efficiency  of  mechanical  ventilation  to  that  of  heat  ventilation,  air  being  dis- 
charged from  the  top  of  the  flue  into  the  outside  atmosphere  of  60  degrees 
temperature. 


Table  showing  Number  of  Times  that  Fan  or  Blower  is  more  Efficient  than  a Chimney 
in  discharging  Air  from  the  Top.  Outside  Temp.,  6o°  F. 


Combined  Efficiency 
Fan  and  Engine. 
Condition. 

Exhaust  Steam  Wasted. 

Exhaust  Utilized 

1 1.3 

Average. 

0.003 

Poorest. 

0.0066 

Average. 

O.OI25 

Best. 

Height  Chimney, 
feet. 

Ratio  of  Efficiencies. 

3° 

9-3 

20.6 

40 

353 

40 

7 

15-5 

30 

262 

5° 

5.6 

I2.4 

24 

212 

60 

4 7 

IO.3 

20 

1 77 

70 

4 

8.9 

17 

I51 

80 

3-5 

7-75 

is 

l33 

90 

3-1 

6.9 

133 

1 18 

100 

2.8 

6 2 

1 2 

106 

Inasmuch  as  the  fan  engine  exhaust  is  almost  universally  utilized,  the 
figures  in  the  last  column  are  indicative  of  the  great  degree  of  superiority  of 
the  fan. 


When  a fan  is  employed  for  the  purpose  of  ventilation,  the  action  is  posi- 
tive, and  air  in  any  required  volume  can  be  handled  without  reference  to  the 
atmospheric  conditions.  Its  use  is  imperative  in  buildings  where  the  per- 
capita  space  is  small  and  the  maximum  air  supply  is  to  be  provided.  The 


6 


MECHANICAL  VENTILATION  AND  HEATING. 


term  “fan,”  as  here  used,  comprehends  only  that  class  of  air-moving  machines 
in  which  air  enters  the  inlet  in  a direction  parallel  to  the  fan  axis,  and  is  dis- 
charged at  the  circumference  in  a direction  at  right  angles  to  the  axis.  Such 
a fan  wheel  is  shown  in  Fig.  2.  The  disc  or  propeller  type  of  wheel,  of  which 
there  are  several  varieties,  has  its  place  as  a ventilating  machine,  but  should 
be  employed  only  where  the  resistances  are  not  great.  It  serves  best  for 
exhausting  purposes,  particularly  where  used  in  connection  with  a heating  and 
ventilating  system  in  which  the  warm  air  is  forced  in  by  a fan  of  the 
centrifugal  type. 

A fan  wheel  of  the  latter  type  is  almost  always  enclosed  in  a steel-plate 
housing  with  proper  inlet  and  outlet  openings.  The  character  of  the  material 
makes  possible  the  ready  construction  of  any  special  form  to  meet  specific 
conditions.  Figs.  3 and  14  represent  leading  types. 


Fig.  3.  Sturtevant  Heating  Apparatus  with  Pulley  Fan. 

It  is  manifest  that  air  may  readily  serve  as  a vehicle  for  heat  for  maintaining 
the  desired  temperature  within  an  apartment.  Evidently  the  air  must  be  pre- 
heated, and  therefore  the  plenum  or  pressure  method  of  supplying  is  preferable 
to  the  vacuum  or  exhaust  method.  All  local  or  direct  heating  surface  is  elimi- 
nated from  the  rooms,  and  may  be  massed  in  connection  with  the  fan,  thereby 
greatly  simplifying  the  details  of  installation.  The  heating  surface  thus  pro- 
vided almost  universally  takes  the  form  of  a steam  coil,  built  up  in  sections  as 
illustrated  in  Fig.  4. 

The  pipes,  usually  one  inch  in  size,  are  here  set  2^6  in.  on  centres,  thus 
providing  a free  area  for  passage  of  air  equal  to  about  40  per  cent,  of  the  gross 
area  of  the  face  of  the  section.  The  air  passing  through  such  a heater  must  be 


MECHANICAL  VENTILATION  AND  HEATING. 


7 


Fig.  4.  Sturtevant  Heater  Sections. 


8 


MECHANICAL  ventilation  and  heating. 


warmed  by  a contact.  The  increment  due  to  radiation  is  very  slight.  Therefore 
the  arrangement  of  pipes  here  shown,  which  thoroughly  breaks  up  all  currents, 
best  serves  the  purpose  by  insuring  intimate  and  constantly  changing  contact. 

The  compactness  of  this  construction  is  shown  by  the  fact  that  within  the 
space  measured  by  6 ft.  in  length,  7 ft.  in  height  and  7^  in.  in  thickness  there 
may  be  massed  nearly  1,000  lineal  ft.  of  one-inch  pipe.  Such  construction 
readily  lends  itself  to  manifold  arrangements  in  connection  with  fans  of  various 
types.  The  most  important  feature  of  this  type  of  combined  heating  and  ven- 
tilating apparatus,  familiarly  known  as  a hot-blast  apparatus,  lies  in  the  fact 
that  the  rapid  movement  of  air  across  the  heated  surfaces  renders  them  vastly 
more  efficient  than  when  exposed  in  still  air.  In  other  words,  far  less  surface 
is  required  for  the  same  heat  transmission. 

The  effect  of  moderate  rates  of  air  movement,  as  determined  by  Prof.  Car- 
penter for  ordinary  indirect  radiators,  shows  that  with  a temperature  differ- 
ence of  150  degrees  and  direct  radiation  in  still  air,  the  heat  transmission  per 
hour  per  degree  difference  is  about  1.85  B.  T.  U.  per  square  foot,  while  with  a 
velocity  of  10  ft.  per  second  it  is  increased  to  about  6 B.  T.  U.  In  other 
words,  the  heating  surface  becomes  over  three  times  as  efficient. 

In  a hot-blast  apparatus  consisting  of  a fan  and  heater  like  those  just  illus- 
trated, the  heat  transmission,  when  the  air  velocity  is  1,200  ft.  per  minute,  is  on 
the  average  about  10  B.  T.  U.,  or  over  5 times  as  much  as  in  the  case  of  direct 
radiation.  That  is,  a hot-blast  apparatus  need  contain  only  one-fifth  the  sur- 
face required  to  secure  a given  result  with  direct  radiation. 

The  effect  of  higher  velocities  and  of  different  steam  pressures  is  well  shown 
by  the  results  of  tests  of  Sturtevant  heaters  in  connection  with  fans.  The 
relative  condensation  increases  with  both  of  these  factors  as  shown  by  the 
curves  for  5 pounds  and  80  pounds  in  Fig.  5.  But  as  indicated  by  the  other  curve, 
the  relative  temperature  increment  with  a given  steam  pressure  decreases  with 
the  velocity.  This  is  the  natural  result  of  moving  a larger  volume  of  air  across 
the  heating  surface,  and  decreasing  the  time  of  contact.  Disregarding  the 
expansion  by  heat,  the  volume  is  proportional  to  the  velocity;  therefore  we  may 
determine  the  relative  heat  transmission  by  multiplying  the  relative  velocity  by 
the  given  condensation. 

The  rate  of  condensation  is  naturally  dependent  upon  the  temperature 
difference  between  air  and  steam,  and  is  therefore  greatest  with  the  maximum 
difference.  Hence  the  less  the  depth  of  the  heater,  the  less  the  total  temper- 
ature increment  of  the  air,  but  the  more  rapid  the  rate  of  transmission  from 
steam  to  air.  With  increasing  depth  of  heater,  or  of  the  number  of  rows  across 


MECHANICAL  VENTILATION  AND  HEATING. 


9 


which  the  air  must  be  passed,  there  is  a corresponding  decrease  in  the  average 
condensation  per  square  foot.  The  surface  first  exposed  to  the  air  of  course 


c 

O 

L 

£ 


(!) 


Velocity  of  Air  Passing  over  Heater  Coils. 


Fig.  5.  Relative  Temperature  Increment  and  Condensation,  for  Different 
Velocities  of  Air  in  Sturtevant  Heater. 


continues  to  maintain  the  same  efficiency,  but  the  surfaces  subsequently  passed 
over  are  progressively  exposed  to  smaller  and  smaller  temperature  differences. 

The  exact  conditions  in  a Sturtevant  heater  operated  in  connection  with  a 
fan  which  produces  a mean  air-velocity  flow  of  1,200  ft.  per  minute  through 
the  free  area  of  the  heater  are  presented  in  Fig.  6. 

From  these  and  the  preceding  curves  it  is  evident  that  the  greatest  surface 
efficiency  is  secured  with  the  highest  velocity  of  air  and  the  least  depth  of 
heater.  Practically,  however,  it  is  necessary  to  limit  the  velocity  of  the  air  and 
to  make  the  heater  of  sufficient  depth  to  give  the  required  temperature  incre- 
ment to  the  air. 

Beyond  a certain  point  the  low  efficiency  of  added  surface  does  not  warrant 
its  introduction.  Furthermore,  in  the  case  of  a building  like  a factory,  so 
sparsely  occupied  that  the  problem  of  heating  is  of  primary  importance,  the 
greatest  economy  in  this  process  will  be  secured  when  the  air  volume  supplied 


o 


MECHANICAL  VENTILATION  AND  HEATING. 


is  the  least,  and  its  temperature  is  the  highest.  In  the  ordinary  building  of 
this  type,  the  air  which  is  actually  required  as  a vehicle  for  the  heat  usually 


Fig.  6.  Relative  Condensation  in  Different  Rows  of  Sturtevant  Heater. 

Velocity  of  Air,  1,200  feet  per  minute. 

exceeds  what  is  necessary  for  the  purposes  of  ventilation.  As  all  air  supplied 
to  the  building  must  necessarily  escape  from  it  at  the  mean  internal  tempera- 
ture, the  opportunity  for  saving  is  apparent. 

A fair  compromise  between  extreme  conditions  and  that  generally  adopted 
in  practice  consists  of  an  arrangement  in  such  a building  whereby  the  fan  is 
operated  at  a circumferential  speed  approaching  5,000  ft.  per  minute.  The 
fan  engine  exhaust  is  utilized.  The  mean  air  velocity. through  the  heater  is 
about  1,800  ft.  per  minute,  and  the  heater  is  of  sufficient  depth  to  warm  the  air 
to  about  140  degrees  in  zero  weather. 

The  design  and  manner  of  application  of  such  an  apparatus,  and  the 
method  of  air  distribution  employed  in  this  system,  must  of  necessity  depend 
upon  the  character  of  the  building,  its  surroundings  and  its  uses.  The 
ordinary  structure  devoted  to  manufacturing  purposes  presents  the  simplest  of 
all  problems.  As  a rule  the  per-capita  space  for  the  operatives  is  large,  and 


MECHANICAL  VENTILATION  AND  HEATING. 


I I 

the  heating  is  to  be  considered  as  of  paramount  importance,  while  the  ventila- 
tion, although  sufficient  with  the  blower  system,  is  in  a sense  incidental.  In 
fact,  ample  ventilation  may  usually  be  secured  by  allowing  the  fan  to  draw  its 
supply  from  the  building  itself,  thereby  simply  turning  the  air  over  and  over, 
and  merely  adding  to  it  the  heat  necessary  to  offset  the  transmission  and 
leakage  losses.  To  this  end  it  is  most  desirable  that  the  apparatus  be  placed 
as  near  the  centre  of  the  building  as  possible,  so  that  the  air  may  be  drawn 
back  to  it  from  all  sides.  Such  location  also  simplifies  the  distributing  system 
and  reduces  the  cost. 


Fig.  7.  Siemens  & Halske  Electric  Co.  of  America,  Chicago,  III. 


From  the  apparatus  the  air  may  be  conducted  by  underground  ducts  or 
overhead  pipes  to  its  proper  destination.  Inasmuch  as  the  best  results  are 
secured  by  discharging  the  heated  air  above  head  level  in  a horizontal  or 
slightly  downward  direction  and  towards  the  outer  walls,  it  is  usually  most  con- 
venient in  a one-story  factory  building  to  carry  the  piping  overhead  in  the 
manner  shown  in  Fig.  7. 

In  this  case  the  apparatus  is  supported  upon  a platform  in  one  corner  of 
the  building,  because  of  the  proximity  of  the  exhaust-steam  supply.  The  hot- 
air piping  is  placed  overhead,  and  carried  entirely  around  the  interior.  Air 
as  a rule  is  returned  from  the  building,  but  the  large  window  area  with  conse- 
quent leakage  is  sufficient  to  bring  about  a constant  air  change  to  meet  all 
purposes  of  ventilation. 

The  fan  in  such  a building  is  usually  operated  at  a maximum  speed  corre- 
sponding to  a circumferential  velocity  of  the  wheel  of  about  a mile  a minute. 
The  velocity  of  discharge  through  the  outlet  in  the  casing  then  approximates 
3,500  ft.,  which,  however,  will  be  decreased  in  proportion  to  the  resistances 
of  the  piping  system.  Although  low  velocities  are  evidently  conducive  to  an 


12 


MECHANICAL  VENTILATION  AND  HEATING. 


economical  movement  of  air,  the  objection  to  large  ducts  necessarily  limits 
their  size,  while  the  customary  utilization  of  the  exhaust  steam  from  the  fan 
engine  reduces  the  possible  saving  to  a very  small  amount. 

For  factory  heating,  the  main  discharge  pipe  leading  from  the  fan  is  gener- 
ally of  the  same  area  as  the  outlet.  The  resistance  of  branches  is  compen- 
sated for  by  increased  area,  so  that  the  aggregate  area  of  the  outlets  will 
range  from  25  to  40  per  cent,  in  excess  of  the  fan  outlet,  and  the  corre- 
sponding discharge  velocities  will  be  decreased  to  2,800  or  2,500  ft.,  or  even 
lower  where  the  resistances  are  great. 

It  is  frequently  possible  in  a building  of  the  character  just  presented,  to 
secure  satisfactory  circulation  of  the  air  with  a limited  extent  of  ducts  by  dis- 
charging the  air  at  high  velocity,  and  thus  compelling  it  to  continue  its  direc- 
tion of  movement  for  a considerable  distance  without  the  use  of  conducting 
pipes.  The  possible  simplicity  of  this  construction  is  largely  due  to  the  char- 
acter of  the  work  carried  on  within  the  building,  especial  refinement  in  the  man- 
ner of  distribution  being  unnecessary  where  the  operatives  are  actively  employed. 

There  are  other  cases,  however,  where,  owing  to  the  presence  of  obstruc- 
tions within  the  building,  the  air  can  be  forced  only  a short  distance  from  the 
pipe  outlet,  and  local  distribution  is  necessary.  Such  is  the  condition  pre- 
sented in  the  ordinary  passenger-car  paint  shop.  Here  the  air  is  discharged 
directly  downward  towaid  the  floor  through  pipes  extending  down  between  the 
cars.  Not  only  is  the  building  effectually  heated,  but  the  time  of  drying  the 
paint  upon  the  cars  is  materially  reduced. 

A similar  problem  presents  itself  in  the  case  of  a locomotive  round  house, 
where  the  fan  system  serves  a double  purpose.  It  effects  a general  heating  of 
the  building  by  discharging  the  air  from  overhead  pipes  toward  the  walls  on 
either  side,  and  at  the  same  time  is  utilized  as  a means  of  rapidly  melting  the 
snow  and  ice  from  the  running  gear  of  the  locomotives.  This  is  done  by 
conducting  a portion  of  the  air  to  the  working  pits. 

In  the  familiar  gallery  type  of  manufacturing  building  the  problem  of  air 
distribution  becomes  somewhat  more  complicated  because  of  the  impossibility 
of  carrying  pipes  across  the  central  space  through  which  the  crane  travels,  or 
of  successfully  forcing  the  air  across  this  space.  It  therefore  becomes  neces- 
sary to  provide  for  distribution  upon  both  sides.  Either  of  two  methods  may 
be  employed.  In  the  former  the  apparatus  discharges  the  air  through  under- 
ground ducts  to  galvanized-iron  flues,  placed  against  the  walls  on  both  sides  of 
the  building.  From  these  the  air  is  delivered  along  the  walls  above  head  level. 

In  the  second  arrangement,  illustrated  in  Fig.  8,  two  independent  appa- 


] 


MECHANICAL  VENTILATION  AND  HEATING.  13 

ratuses  are  employed.  They  are  placed  in  the  galleries  midway  of  the  length 
of  the  building,  and  each  delivers  the  air  to  a double  system  of  pipes,  one  for 
each  floor,  whence  it  is  discharged  toward  the  outer  walls.  This  is  an  ideal 
arrangement  for  the  return  and  reheating  of  the  air. 

In  any  installation  the  first  cost  is  dependent  upon  the  number  of  indi- 
vidual units  in  the  heating  system.  In  the  ordinary  building  a single  appa- 
ratus is  usually  most  desirable,  but  when  numerous  connected  structures  are 
to  be  warmed,  it  is  generally  expedient  to  divide  this  into  a number  of 
independent  units. 


In  buildings  of  more  than  one  story,  the  simplest  arrangement  for  heating 
consists  in  placing  the  apparatus  on  the  lower  floor  or  in  the  basement,  and 
delivering  the  air  into  one  or  more  vertical  flues  from  which  it  is  discharged 
through  suitable  outlets  upon  the  several  floors.  In  a wooden  structure,  or  in 
one  of  brick  or  stone  which  is  already  built,  such  distribution  must  be  made  by 
means  of  galvanized  iron  pipes. 

The  simplest  possible  arrangement  consists  of  a single  upright  galvanized- 
iron  flue,  immediately  beneath  which  the  apparatus  is  placed  so  as  to 
deliver  the  air  directly  upward  into  the  base  of  the  flue.  Upon  each  floor 
the  requisite  number  of  outlets  are  provided  at  or  near  ceiling  level  and  the 
air  discharged  therefrom  towards  the  outer  walls.  In  the  case  presented  in 


MECHANtCAL  VENTILATION  AND  HEATING. 


Fig.  9.  Rochester  Optical  Co.,  Rochester,  N.  Y. 


mechanical  ventilation  and  HEATING.  13 

Fig.  9,  adjacent  rooms  are  thus  heated  with  the  minimum  amount  of  distrib- 
uting pipe.  It  is  evident  that  a similar  arrangement  may  be  introduced  within 
a building  of  the  same  floor  area,  but  without  such  partition  wall,  in  which  case 
the  pipe  would  be  located  practically  in  the  centre.  Or  distribution  may  be 
made  from  a vertical  pipe  placed  against  one  of  the  walls,  the  effect  then  being 
equivalent  to  that  secured  within  that  portion  of  this  particular  building  in 
which  the  pipe  is  shown  to  be  located. 

As  the  building  becomes  more  extended  in  its  character,  it  becomes  neces- 
sary with  a single  standpipe  system  to  somewhat  extend  the  branches  so  as  to 


convey  the  air  to  a greater  distance  from  the  standpipe,  as  is  clearly  shown  in 
Fig.  10.  The  apparatus  is  here  placed  in  the  basement  and  discharges  directly 
upward  into  the  standpipe.  Upon  the  first  floor  the  branch  pipe  is  extended 
and  subdivided  so  as  to  heat  the  individual  offices  on  that  floor,  while  upon 
the  other  floors  the  horizontal  branch  is  only  of  moderate  length.  In  a long 
building  in  which  a single  standpipe  is  adhered  to,  a greater  extent  of  the 
piping  system  on  each  floor  may  be  made,  as  in  the  case  of  Fig.  n,  where  the 
standpipe  is  carried  up  outside  of  the  building,  but  thoroughly  protected,  and 
the  horizontal  pipes  on  the  various  floors  are  kept  comparatively  near  the  wall. 
Evidently  a similar  arrangement  can  be  made  if  the  standpipe  is  carried  up  in 


1 6 


MECHANICAL  VENTILATION  AND  HEATING. 


Fig.  ii.  Montmorency  Cotton  Mills,  Montmorency,  P.  Q. 


MECHANICAL  VENTILATION  AND  HEATING. 


l8  MECHANICAL  VENTILATION  AND  HEATING. 

the  centre  of  the  building  and  the  pipes  extended  lengthwise  therefrom  on 
each  floor. 

Where  the  available  floor  area  will  permit,  fully  as  simple  an  arrangement 
is  that  presented  by  Fig.  13  in  which  three  individual  standpipes  are  provided, 
each  discharging  air  through  several  outlets  near  ceiling  level  and  always 
towards  the  outer  walls.  The  apparatus  used  in  this  instance  consists  of  a 
fan  of  the  ^-housing  type  with  a portion  of  the  scroll  built  in  the  brick 
foundation,  a heater  of  the  construction  previously  illustrated  in  Fig.  4,  and  a 
horizontal  engine  direct  connected  to  the  fan  shaft,  all  as  illustrated  in  Fig.  14. 


Pig.  14.  Sturtevant  Heating  Apparatus  with  ^-Housing  Steam  Fan. 

In  a new  brick  building,  convenience  can  be  secured  by  distributing  the  air 
from  one  or  more  brick  flues  built  against  the  wall  of  the  building.  If  these 
are  provided  in  sufficient  number  they  require  no  distributing  pipe  connections, 
but  if  economy  is  sought  by  providing  a single  flue,  then  it  becomes  necessary 
to  obtain  satisfactory  distribution  on  each  floor  in  some  such  manner  as  is 
shown  in  Fig.  12,  in  which  an  individual  system  is  provided  at  the  ceiling  of 
each  floor.  Where  the  building  is  of  less  extent,  a special  deflecting  outlet  may 
be  placed  upon  the  opening  in  the  flue  on  each  floor  and  serve  to  effectually 
distribute  the  air. 

In  a new  brick  structure  of  reasonable  size,  the  best  arrangement  consists 


MECHANICAL  VENTILATION  AND  HEATING. 


9 


in  building  a series  of  pilaster  flues  against  the  outer  wall  along  one  side  of  the 
building,  from  each  of  which  the  air  is  discharged  toward  the  opposite  side 
through  openings  at  eight  or  more  feet  above  the  floor.  The  modern  textile 
mill  with  its  symmetrical  design  is  manifestly  adapted  for  such  an  arrangement. 


The  apparatus  is  usually  placed  in  the  basement,  near  the  centre  of  the 
building,  and  discharges  the  air  into  a duct  running  along  one  side  of  the  build- 
ing, and  communicating  with  the  bases  of  the  flues,  as  illustrated  in  Figs.  15 
and  16. 

These  flues  add  but  little  to  the  cost  of  the  building.  Each  opening  or 
outlet  is  provided  with  a special  form  of  damper,  Fig.  17,  which  serves  the 
double  purpose  of  deflecting  the  air  toward  the  room  when  open,  and  of 
preventing  admission  when  closed. 

The  large  amount  of  moving  machinery,  pulleys,  shafting  and  belts  in  such 
a building  serves  to  thoroughly  break  up  all  air  currents  and  effectually  distribute 
the  air.  The  equality  of  temperature  maintained  is  evidenced  by  the  accom- 
panying average  results  and  readings  taken  at  random  from  a record  kept  at 
the  West  Weave  Shed  of  the  Pacific  Mills,  Lawrence,  Mass. 


20 


mechanical  ventilation  and  heating. 


Temperature  and  Humidity  in  West  Weave  Shed,  Pacific  Mills, 
Lawrence,  Mass. 


Date. 

Time. 

East 

End. 

Temperature. 

Middle. 

West 

End. 

> 

b 

O 

X 

Floor. 

Head 

High. 

Ceiling. 

1889. 

Degrees. 

Degrees. 

Degrees. 

Degrees. 

Degrees. 

Per  Cent 

Feb.  7 . . . . 

9:15  A.  M. 

70 

70 

70 

71 

68 

65 

Feb.  7 . . . . 

1:15  P.  M. 

68 

69 

68 

70 

66 

64 

Feb.  7 . . . . 

6:15  P.  M. 

70 

71 

7i 

72 

66 

66 

Feb.  8 . . . . 

6:45  A.  M. 

70 

69 

7i 

73 

66 

61 

Feb.  8 . . . . 

2:45  P-  M. 

73 

74 

75 

76 

72 

68 

Feb.  9 . . . . 

7:25  A.M. 

70 

69 

7 1 

72 

66 

75 

Feb.  11  ...  . 

10:30  A.  M. 

68 

68 

69 

68 

68 

75 

Feb.  11.... 

•% 

5:30  P.  M. 

72 

72 

73 

72 

69 

63 

Average 

70.12 

70.25 

72.25 

71-75 

67.64 

67.12 

Comparative  Cost  and  Running  Expenses  for  Heating,  Ventilating  and 
Moistening  System,  Globe  Yarn  Mills,  Nos.  i and  2, 

From  Oct.  15,  1888,  to  March  15,  1889. 


Cost  of  Introduction. 

No.  1.  * 

No.  2.  t 

First  cost  of  heating  and  moistening  system 

First  cost  heating,  ventilating  and  moistening  system  .... 

$4,600.00 

1,103,852 

$4,000  00 

Cubic  contents,  cubic  feet 

1,316,52° 

Average  temperature 

70° 

78° 

Cost  of  system  per  1,000  cubic  feet 

$4-17 

$3-°  4 

Ratio | 

IOO 

I37 

73 

IOO 

Running  Expenses. 


Coal  burned  for  heating 

Coal  burned  for  moistening 

Coal  burned  for  both  heating  and  moistening  . 

Coal  burned  for  heating,  ventilating  and  moistening 
Coal  burned  per  1,000  cubic  feet 

Ratio 


317,100  lbs.  i 

58,500  lbs.  1 . . . . 

375,600  lbs. 

286,900  lbs. 

340.26  lbs.  217.92  lbs. 
j 100  64 

t 158  1 00 


* Overhead  direct  radiation  and  Garland  moistening  system, 
t Sturtevant  system  of  heating,  ventilating  and  moistening. 


MECHANICAL  VENTILATION  AND  HEATING. 


Ti’  e mill  was  440  ft.  long  and  70  ft.  wide.  The  west  end 
was  entirely  exposed  to  the  sweeping  winds  from  the  Merrimac 
River,  while  the  east  end  contained  the  lighting  plant  and 
heating  apparatus.  The  openings  for  air  admission  were  only 
five  in  Lumber  on  each  floor,  placed  along  the  south  side  of 
the  mill,  and  aggregating  2.37  square  inches  area  per  1,000 
cubic  feet  of  space. 

An  im)  ortant  advantage  of  the  blower  system  in  the  textile 
mill  lies  i 1 the  opportunity  presented  for  moistening  the  air 
so  as  to  >ffset  the  serious  effect  of  frictional  electricity  gen- 
erated 1 y the  motion  of  belts,  pulleys,  running  stock  and 
machim  ry.  In  a direct-heated  mill  the  moistening  arrange- 
ments rre  frequently  very  expensive. 

An  interesting  comparison  of  first  costs  and  running 
expen:  es  in  two  nearly  identical  mills  belonging 
to  the  same  corporation  is  here  presented.  Mill 
No.  1 was  heated  by  direct  radiation,  and  a com- 
plete independent  moistening  system  was  intro- 
duce 1.  In  Mill  No.  2 the  blower  system  was 
inst  lied  for  the  combined  purposes  of  heating, 


Fig.  16. 


-3 


ventilating  and  moistening.  The  cubic  contents  of 
the  latter  building  was  the  greater,  as  was  also  the 
exposure.  Nevertheless,  the  first  cost  of  the  system 
per  1,000  cubic  feet  was  only  73  per  cent,  of  that  in 
the  No.  1.  Mill,  while  the  temperature  maintained  was 
much  higher,  with  a fuel  expenditure  of  only  64  per 
cent,  of  that  required  in  Mill  No.  1.  Although  the 
air  supply  was  taken  from  the  building,  the  natural 
leakage  was  so  great  as  to  provide  ample  ventilation. 

In  all  the  buildings  of  the  types  thus  far  presented 
the  ventilation  has  been  of  secondary  importance,  but 
in  a large  class  of  structures,  more  or  less  public  in 
their  character,  such  as  schools,  churches,  theatres  and  halls,  where 
the  occupants  are  more  or  less  closely  seated,  the  per-capita  space  is 
comparatively  small,  and  the  vitiation  by  respiration  proportionately 
great.  The  animal  heat  of  the  occupants  has  a material  effect  in  warm- 
ing the  room,  and  in  a building  like  a theatre,  which  has  practically 
no  exposed  walls,  the  problem  of  artificial  heating  is  thereby  reduced 


Fig.  17. 


22 


MECHANICAL  VENTILATION  AND  HEATING. 


to  relative  insignificance.  The  ventilating  problem,  however,  assumes  corres- 
pondingly increased  importance,  and  it  becomes  necessary  to  provide  means 
of  supplying  air  in  large  volumes,  properly  tempered,  admitted  at  such  low 
velocity,  and  in  such  location  as  to  avoid  all  possibility  of  drafts.  Positive 
means,  unaffected  by  atmospheric  changes,  must  be  adopted.  The  fan  blower 
is  now  generally  recognized  as  the  only  device  which  will  satisfactorily  meet 
these  requirements.  Proper  results  can  only  be  obtained  when  it  is  installed  to 
operate  on  the  plenum  system  by  forcing  the  air  into  the  building.  It  is  then 
both  convenient  and  necessary  to  heat  the  air  in  transit  to  the  rooms,  but 
inasmuch  as  the  temperature  and  air- supply  requirements  are  likely  to  vary  in 
the  different  rooms,  some  means  more  refined  than  is  possible  in  factory  heating 
must  be  employed  for  their  proper  regulation.  Any  one  of  three  methods  may 
be  employed. 


Fig.  i 8.  Heating  and  Ventilating  Apparatus  for  Hot  and  Cold  System. 

First. — The  air,  properly  tempered,  may  be  admitted  in  constant  volume, 
and  temperature  regulation  within  the  room  secured  by  the  use  of  direct 
radiators. 

Second. — The  air  discharged  from  the  fan  at  constant  volume  and  tempera- 
ture may  be  heated  to  any  desired  degree  by  supplementary  steam  coils  placed 
within  the  supply  ducts  to  the  various  rooms. 

Third. — The  entire  heating  surface  may  be  concentrated  in  connection  with 
the  fan  operating  at  constant  speed,  and  so  arranged  that  the  air  discharged 
through  it  will  be  heated,  while  other  air  by-passed  round  it  still  remains  cool. 
A mixture  of  the  warm  and  the  cool  air  may  then  be  made  in  any  desired  pro- 
portions to  meet  the  exact  requirements  of  the  individual  rooms. 

An  apparatus  arranged  in  this  general  manner  is  shown  in  Fig.  18. 

From  the  hot  and  cold  outlets  of  such  an  apparatus  separate  ducts  convey 
the  air  to  the  bases  of  the  ventilating  flues  in  the  rooms,  connecting  as  in  the 


MECHANICAL  VENTILATION  AND  HEATING. 


23 


illustration  of  a modern  school  building,  presented  in  Fig.  19.  The  flues  are  in 
the  interior  walls,  and  are  provided  with  openings  8 ft.  or  more  above  the 
floor.  From  each  outlet  the  air  is  discharged  at  low  velocity  toward  the  cold 
outer  walls,  where  it  becomes  slightly  cooled,  falls,  and  passes  with  slow  move- 
ment back  across  the  bodies  of  the  occupants  to  the  vent  opening,  which  is  at 
the  floor  level  in  the  interior  wall  and  near  the  supply  flue. 

With  this  arrangement,  proper  mixture  of  the  warm  and  cool  air  at  the  flue 
base  results  from  the  action  of  mixing  dampers  operated  by  hand  or  auto- 
matically controlled.  The  arrangement  of  flue,  hot  and  cold  air  pipes,  and 
hand-operated  mixing  damper  is  shown  in  the  sectional  detail  on  the  left. 

This  system  is  familiarly  known  as  the  hot  and  cold  system.  As  ordinarily 
installed,  the  hot  and  cold  air  connections  to  each  mixing  damper  are  of  equal 
size,  so  that  wheth  ir  the  air  be  hot  or  cold,  or  a mixture  of  the  two,  its  volume 
will  remain  constant. 

Another  arrangement  of  the  hot  and  cold  system  with  forced  circulation 
consists  in  mixing  the  air  at  the  heating  chamber,  and  thence  forcing  it,  prop- 
erly tempered,  though  individual  pipes  to  the  ventilated  rooms.  In  the  design 
of  the  apparatus  a tempering  coil  is  provided,  so  that  all  the  air  is  warmed  to  a 
temperature  never  exceeding  70  degrees.  The  main  heater  is  enclosed  in  a 
brick  chamber,  and  is  supported  above  the  floor  at  such  height  that  a portion 
of  the  air  may  pass  beneath  without  receiving  supplementary  heating.  Indi- 
vidual automatic  thermostats  control  the  proportions  of  the  mixture. 

Although  carbon-dioxide  or  carbonic-acid  gas  is  the  principal  product  of 
respiration,  it  is  by  no  means  the  most  harmful.  The  true  evil  of  a vitiated 
atmosphere  lies  in  its  other  constituent  gases  and  micro-organisms,  which, 
however,  are  difficult  of  determination.  Fortunately  they  preserve  a fairly 
constant  proportion  to  the  amount  of  carbonic  acid  present.  As  this  gas  is 
readily  determinable,  its  relative  amount  in  a given  volume  of  ai*r  is  generally 
accept  d as  a measure  of  its  purity. 


Cubic  feet  of  air 
containing  four 
parts  of  car- 
bonic acid  in 
10,000  supplied 
per  person. 

Per 

Hour. 

1 6000 

4000 

3000 

2400 

2000 

1800 

1714 

I5°° 

1200 

IOOO 

525 

375 

231 

Per 

Min. 

100 

66.6 

So 

4° 

33-3 

30 

28.6 

25  I 

20 

l6.6 

9.1 

1 

6.2 

3-8 

Degree  of  vitia- 
tion of  the  air 
in  the  room. 

Parts  of  car- 
bonic acid 
in  10,000. 

5 

5-5 

6 

6.5 

7 

7-33 

7-5 

8 

9 

IO 

*5 

20 

30 

24 


MECHANICAL  VENTILATION  AND  HEATING, 


19.  Agassiz  School,  Boston,  Mass. 


MECHANICAL  VENTILATION  AND  HEATING. 


25 


Assuming  four  parts  of  carbonic  acid  in  10,000  parts  of  air  as  the  normal 
vitiation  of  the  external  atmosphere,  and  of  a cubic  foot  per  hour  as  the 
amount  of  carbonic  acid  exhaled  by  an  average  person,  we  have  the  accom- 
panying requirements  regarding  the  air  supply  necessary  to  maintain  a given 
standard  of  purity  within  an  apartment. 

A supply  of  30  cubic  feet  per  person  per  minute,  by  which,  under  these  con- 
ditions, the  degree  of  vitiation  is  maintained  at  7 33  parts  carbonic  acid  in 
10,000  of  air,  has  been  very  generally  accepted  as  the  minimum  volume  per- 
missible for  the  requirements  of  what  may  be  considered  good  ventilation. 
This  marks  the  practical  limit  of  the  most  successful  systems  where  mechanical 
means  are  not  employed.  In  point  of  fact  the  average  for  such  systems  is  well 
below  this  amount. 

Under  good  school-room  conditions,  with  a space  allowance  of  250  cubic 
feet  per  occupant,  a supply  of  50  cubic  feet  per  minute,  or  3,000  cubic  feet 
per  hour  per  individual,  appears  to  mark  the  practical  limit  of  success  for 
imperceptible  admission  of  air.  This  is  equivalent  to  changing  the  entire 
volume  within  the  room  once  in  five  minutes.  Increased  volumes  call  for 
increased  care  in  the  manner  of  introduction,  as  evidenced  in  lower  velocities 
and  the  greater  extent  of  inlet  openings. 

When  we  consider  that  every  child  has  a money  value,  represented  by  the 
expenditure  necessary  to  develop  him  to  his  present  physical  and  mental 
condition,  and  a potential  value  as  a future  wage  earner,  which  death  or 
physical  decline  will  make  a total  loss,  the  business  aspect  of  school-room 
ventilation  becomes  evident. 

Viewed  from  the  financial  standpoint  alone,  the  actual  cost  of  improved 
ventilation  must  be  considered  in  its  relation  to  the  benefits  derived  therefrom. 
Obviously  this  cost  must  vary  with  the  degree  of  ventilation,  but  the  following 
figures  from  reports  of  the  School  Committee  of  the  city  of  Boston  have  suffi- 
cient relative  importance  to  be  conclusive.  During  the  school  year  ending 
June  30,  1893,  the  total  expenditure  per  pupil  in  the  Boston  public  schools, 
exclusive  of  furniture,  repairs  and  new  schoolhouses,  was  $25.10.  Of  this 
amount  $0,945  was  expended  for  fuel,  so  that  the  proportional  cost  of  both 
heating  and  ventilating  was  only  3.75  per  cent,  of  the  total  annual  expense  for 
the  education  of  the  child. 

During  the  year  covered  by  this  report,  the  degree  of  air  purity  maintained 
in  these  schools  was  by  no  means  up  to  the  requirements  of  even  fair  ventila- 
tion. A conservative  estimate  would  indicate  that  their  heating  alone  might 
have  been  attained  at  an  expense  of  about  82  cents  per  pupil.  The  ventila- 


26 


MECHANICAL  VENTILATION  AND  HEATING. 


tion,  such  as  it  was,  and  for  the  hours  of  occupancy  only,  therefore  cost  about 
12^4  cents  per  pupil  for  the  entire  year.  Fair  ventilation,  secured  by  the 
supply  of  30  cubic  feet  of  air  per  minute  per  pupil,  would  have  cost  not  over  33 
cents  per  pupil,  making  the  total  cost  about  $1.15  per  pupil  for  both  venti- 
lation and  heating.  The  additional  expenditure  necessary  to  bring  the  Boston 
schools  up  to  a uniform  standard  of  fair  ventilation  would  therefore  have 
entailed  an  increased  annual  expense  for  fuel  of  only  20^  cents  per  pupil,  or 
less  than  of  one  per  cent,  of  the  total  annual  expense  of  education. 

Ordinary  practice  in  school-house  heating  and  ventilation,  as  exemplified  in 
the  illustration  previously  presented,  limits  the  fan  speed  to  that  required  to 
produce  about  one-half  ounce,  or  ^4  in.  pressure  per  square  inch,  equivalent  to 
a tip  velocity  of  the  wheel  of  about  3,600  ft.  per  minute.  Duct  velocities  will 
then  range  from  1,200  or  1,500  up  to  2,000  ft.  per  minute,  flue  velocities  from 
500  to  800  ft.,  and  velocities  of  discharge  to  rooms  from  300  to  400  ft. 

All  classes  of  buildings  which  may  be  properly  included  within  the  term 
“ halls  of  audience  ” require  substantially  equal  volumes  of  air  to  maintain 
equivalent  degrees  of  purity,  but  their  character,  the  per-capita  space  and  the 
arrangements  for  seating  largely  control  the  manner  of  admission  of  air. 
Where  the  seats  are  permanently  fixed  and  a plenum  space  can  be  provided 
beneath  the  floor,  the  air  may  be  admitted  therefrom  through  a multitude  of 
small  openings,  thence  pass  upward  across  the  persons  of  the  occupants, 
and  escape  through  ceiling  openings.  It  thus  becomes  heated  in  transit  and, 
in  the  case  of  an  auditorium  having  little  or  no  external  exposure,  must  be 
admitted  at  a temperature  measurably  below  that  to  be  maintained  within  the 
room. 

A counter  direction  of  movement  is  sometimes  provided,  the  air  discharged 
by  the  supply  fan  being  admitted  through  a perforated  ceiling  and  drawn  down 
through  the  floor  by  an  auxiliary  exhaust  fan. 

As  a rule  neither  of  these  methods  is  admissible  in  a building  diversified  in 
its  uses,  like  a city  hall,  for  instance.  For  the  smaller  rooms,  a so-called 
corridor  system  of  distribution  may  be  employed,  the  pipes  being  carried  in 
spaces  formed  by  furring  down  the  corridor  ceilings.  Air  is  thus  readily 
admitted  above  head  level  and  discharged  toward  the  outer  walls.  Leakage 
to  the  corridors  and  to  the  outer  atmosphere  usually  meets  the  requirements 
of  ventilation  under  the  conditions  of  pressure  maintained  by  the  fan. 

Plenum  spaces  beneath  the  audience  chamber,  which  is  almost  universally 
placed  above  the  offices,  are  here  out  of  the  question,  and  the  simplest  practi- 
cable arrangement  consists  in  admitting  air  from  wall  registers  beneath  the 


MECHANICAL  VENTILATION  AND  HEATING. 


27 


gallery,  and  upon  either  side  of  the  stage,  and  then  providing  ventilation 
through  wall  registers  near  floor  level,  as  well  as  through  ceiling  openings. 
The  per-capita  space  is  usuallyTimited,  and  under  the  conditions  it  is  difficult 
to  imperceptibly  admit  sufficient  volumes  of  air. 

A church  presents  conditions  peculiar  to  itself,  for  the  per-capita  space  is 
usually  large,  the  heat  transmission  losses  are  excessive,  the  time  of  occupancy 
is  slight,  and  the  period  of  heating  is  frequently  limited  to  a few  hours  upon 
Sunday  only.  Although  floor  supply,  subdivided  for  the  individual  pews,  forms 
an  ideal  arrangement  in  such  a building,  it  is  frequently  difficult  of  introduction 
and  usually  expensive. 

A simpler  arrangement,  decidedly  effective  in  its  application,  consists  in 
admitting  the  air  through  wall  registers,  supplied  from  a system  of  piping 
beneath  the  floor.  The  greater  part  escapes  though  ventilating  registers  at 
floor  level. 

One  of  the  most  complicated  problems  presented  to  the  heating  and  venti- 
lating engineer  is  that  of  the  modern  theatre.  Consisting  as  it  does  of  three 
principal  parts,  namely,  the  auditorium  proper,  the  stage  and  dressing-rooms, 
and  the  foyer,  lobbies,  stairways  and  connecting  apartments,  there  is  opportu- 
nity for  constantly  changing  conditions  as  the  performance  progresses.  It  is 
seldom  that  the  auditorium  of  a building  of  this  character  has  any  exposed 
walls.  The  effect  of  the  occupants  and  of  the  lighting  medium  is  therefore  to 
increase  the  temperature  to  such  an  extent  that  the  air  must  be  admitted  at  a 
temperature  below  the  normal,  in  order  to  maintain  a comfortable  standard. 

Wall  admission  of  air  in  large  volumes  is  therefore  impracticable,  for  the 
cooler  air  tends  to  fall  with  disastrous  results  to  the  audience.  Floor  or  ceil- 
ing supply  presents  the  only  successful  solution.  As  a rule  the  former  method 
is  more  readily  and  economically  introduced.  A practical  application  is 
presented  in  Fig.  20. 

Located  in  the  space  beneath  the  foyer  and  lobbies,  at  a point  convenient 
to  the  fresh  air  supply  from  above  the  roof,  is  the  heating  apparatus.  The  air 
(heated  or  otherwise,  as  may  be  necessary),  as  it  leaves  the  fan,  passes  in 
properly  proportioned  volumes  in  either  direction  along  the  passage,  whence  the 
greater  part  is  allowed  to  escape  to  the  space  beneath  the  auditorium  proper. 
In  smaller  volumes  it  is  delivered  to  the  first  and  second  balconies  through  flues 
in  the  pilasters  and  through  the  hollow  walls  at  the  rear  of  the  auditorium. 
Through  the  large  flues,  near  the  boxes,  and  upon  either  side  of  the  auditorium, 
air  passes  to  large  wall  registers,  as  shown  in  the  section,  and  also  to  the  space 
beneath  the  second  balcony  floor.  The  boxes  are  supplied  through  special 


MECHANICAL  VENTILATION  AND  HEATING. 


Fig.  20.  Castle  Square  Theatre,  Boston,  Mass. 


MECHANICAL  VENTILATION  AND  HEATING. 


29 


flues,  which  discharge  into  the  passages  with  which  they  connect,  whence  the 
air  enters  the  boxes  beneath  the  doors,  which  are  cut  short,  and  passes  across 
the  occupants  to  the  body  of  the  house. 

The  principal  supply  for  the  auditorium  — amounting  to  nearly  30,000  cubic 
feet  per  minute  for  the  orchestra  and  orchestra  circle  alone,  and  as  much  more 
for  the  balconies — is  admitted  through  the  floors  of  these  respective  portions. 
In  the  case  of  the  main  floor,  the  space  beneath  it  permits  of  the  ready  distri- 
bution of  the  air  admitted  thereto  through  the  numerous  openings  in  the  base- 
ment partition  wall. 

The  chair  legs  throughout  the  entire  house  are  provided  with  special  latticed 
castings,  forming  thereby  a large  number  of  air  chambers  to  which  air  is  dis- 
charged through  the  floor  openings.  The  air  thus  passing  through  the  floor 
openings  at  relatively  high  velocity  is  permitted  to  escape  beneath  the  persons 
of  the  occupants  with  low  and  imperceptible  movement,  and  then  pass  upward 
to  the  ceiling  vents. 

These  vents,  consisting  of  a central  ceiling  opening  of  moderate  size  and 
numerous  smaller  openings  in  the  ceiling  at  the  back  of  the  second  balcony, 
provide  for  a backward  sweeping  movement  of  the  air  across  both  first  and 
second  balconies,  thereby  securing  the  highest  efficiency  from  a given  volume 
of  air.  Special  ventilation  from  the  orchestra  circle  and  the  extreme  rear  of 
the  first  balcony  is  also  indicated  in  the  sectional  view.  From  the  roof  space 
to  which  all  this  foul  air  passes,  it  is  exhausted  by  a large  electrically  driven 
cone  fan,  located  upon  the  roof  above  the  stage  and  discharging  freely  into  the 
atmosphere. 

All  escape  of  odors  from  the  toilet  and  smoking  rooms  to  other  apartments 
is  avoided  by  providing  special  and  positive  exhaust  ventilation  therefrom  by 
means  of  an  exhaust  fan,  located  in  the  basement,  which  connects  with  a series 
of  vertical  flues.  The  same  fan  also  serves  to  remove  the  heated  air  and 
odors  from  the  kitchen  and  the  boiler  and  dynamo  rooms  beneath  the  hotel. 

The  foyer  is  supplied  with  warm  air  through  registers  in  the  walls  beneath 
the  stairs,  and  is  independently  ventilated  through  its  triple-domed  ceiling. 
The  stage  is  heated  by  means  of  steam  coils  at  the  back,  suspended  just 
beneath  the  floor,  cast-iron  gratings  being  provided  through  which  the  heated 
air  may  pass  upward. 

The  temperature  throughout  the  auditorium  is  regulated  by  a thermostat 
arranged  to  operate  a by-pass  damper  on  the  heater,  so  that  any  desired  tem- 
perature of  the  air  passing  to  the  conduit  may  be  secured.  To  avoid  trouble 
from  too  great  and  sudden  cooling  of  the  air,  a minimum  thermostat  is  also 


30 


MECHANICAL  VENTILATION  AND  HEATING. 


introduced,  which,  as  usually  set,  prevents  the  admission  of  air  to  the  auditorium 
at  a temperature  lower  than  65  degrees.  With  this  arrangement  this  tempera- 
ture is  readily  and  uniformly  maintained  at  70  degrees  throughout  the  house, 
while  30  cubic  feet  and  over  is  supplied  per  minute  to  each  occupant. 

The  conditions  presented  in  a modern  retail  store  are  peculiar,  in  that  the 
effect  of  constant  passing  through  the  doors  is  to  admit  large  volumes  of  cold 
air,  which  very  materially  chill  the  adjacent  portions  of  the  store.  This  may 
be  obviated  to  a very  great  extent  by  providing  vestibules  which  are  kept 
thoroughly  warm  by  hot  air  supplied  under  pressure,  so  that  all  leakage  is  out- 
ward, and  by  introducing  air  at  floor  level  beneath  the  counters  facing  or  near 
the  doors. 


Fig.  21.  Heating  System  in  the  Office  Building  of  the  American  Bell 
Telephone  Co.,  Boston,  Mass. 


Where  the  store  is  open  in  its  character,  the  air  may  be  delivered  to  the 
various  floors  through  vertical  brick  flues  located  in  the  centre  of  the  building 
or  in  the  side  walls,  and  distributed  on  individual  floors  by  deflecting  outlets. 

In  an  office  building  of  several  stories  an  arrangement  like  that  shown  in 
Fig.  2 1 serves  for  thorough  distribution,  the  apparatus  being  placed  in  the 
basement  and  discharging  the  air  into  a vertical  flue  with  connections  to 
horizontal  ducts  on  each  floor.  These  ducts  are  arranged  on  the  corridor 
system  previously  mentioned,  the  admission  to  each  room  being  made  at  or 
near  the  ceiling. 


MECHANICAL  VENTILATION  AND  HEATING. 


31 


On  ship-board  the  subject  of  proper  ventilation  is  receiving  the  attention 
it  has  so  long  deserved,  and  systems  have  been  introduced  in  our  trans- 
Atlantic  liners  on  the  general  principles  already  described. 

The  public  at  large  is  not  slow  to  appreciate  the  material  benefits  of  good 
ventilation,  but  its  unsatisfactory  experience  with  the  movement  of  air  by 
natural  methods  has  almost  led  it  to  question  whether  good  ventilation  is 
attainable.  Evidently  positive  means,  acting  independently  of  the  weather,  and 
capable  of  moving  the  required  volumes,  are  absolutely  necessary  to  success. 
The  centrifugal  fan  best  meets  these  conditions.  It  is  furthermore  a most 
important  factor  in  the  interdependent  system  which  has  been  under  discussion. 

The  particular  features  of  this  combined  system  of  ventilation  and  heating 
may  be  thus  summarized.  The  entire  heating  surface  is  centrally  located, 
enclosed  in  a fire-proof  casing,  and  placed  under  the  control  of  a single  indi- 
vidual, thereby  avoiding  the  possibility  of  damage  by  leakage  or  freezing  inci- 
dent to  a scattered  system  of  steam  piping  and  radiators.  The  heater  itself  is 
adapted  for  the  use  of  either  live  or  exhaust  steam,  and  provision  is  made  for 
utilizing  the  exhaust  of  the  fan  engine,  thereby  reducing  the  cost  of  operation 
to  practically  nothing.  At  all  times  ample  and  positive  ventilation  may  be 
provided  with  air  tempered  to  the  desired  degree.  Absolute  control  may  be 
had  over  the  quality  and  quantity  of  air  supplied.  It  may  be  filtered  and 
cleansed,  heated  or  cooled,  dried  or  moistened  at  will.  By  means  of  the  hot 
and  cold  system,  the  temperature  of  the  air  admitted  to  any  given  apartment 
may  be  instantly  and  radically  changed  without  the  employment  of  supple- 
mentary heating  surface. 

The  pressure  created  within  the  building  is  sufficient  to  cause  all  leakage 
to  be  outward,  preventing  cold  inward  drafts  and  avoiding  the  possibility  of 
drawing  air  from  any  polluting  source  within  the  building  itself.  By  returning 
the  air,  using  live  steam  in  the  heater  and  operating  the  fan  at  maximum  speed, 
a building  may  be  heated  up  with  great  rapidity,  as  is  usually  desirable  in  the 
morning. 

The  area  of  heating  surface  is  only  one-third  to  one-fifth  that  required  with 
direct  radiation,  while  the  primary  cost  and  operating  expense  of  a fan  is  far 
less  than  that  of  any  other  device  for  moving  the  same  amount  of  air. 

The  system  is  essentially  a necessity  in  buildings  occupied  as  halls  of 
audience,  and  may  be  readily  introduced  in  the  mill  and  the  factory.  The 
increasing  extension  of  electric  power  and  fuel-gas  distribution  is  making  pos- 
sible its  application  in  all  classes  of  buildings.  Full  appreciation  of  its  advan- 
tages is  therefore  the  best  guarantee  of  its  introduction. 


